Constant current class 3 lighting system

ABSTRACT

A flexible cable is provided for a lighting system having a power supply that includes a power supply input to receive a first signal having a first frequency and a circuit for converting the first signal to a second signal, and at least one luminaire coupled to a lamp driver. The cable comprises a first leg of wires for carrying the second signal. The first wire electrically connects a loop output of the power supply to an input of the lamp driver and a second wire electrically connects an output of the lamp driver to a loop return of the power supply. The cable further comprises a second leg of wires electrically connected to a ground of the power supply and the ground of the lamp driver. The second signal has a substantially constant current and a second frequency distinctly higher than the first frequency. The flexible cable further comprises a modular connector.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a division of co-pending U.S. application Ser. No. 10/799,741,filed on Mar. 12, 2004, which is incorporated herein by reference to theextent permitted by law.

BACKGROUND

The National Electrical Code defines three classes of circuits andprovides specific installation requirements for each. In general, Class2 is defined as any circuit that provides 30V or less at 100 VA. Class 3is defined as any circuit that provide up to 150V at 100 VA. Class 1 maythen be used to classify circuits that provide output that is not powerlimited.

Lighting systems typically consist of permanently wired-in lightingfixtures, with each lighting fixture obtaining its power directly from aregular Class 1 power line. As a regular power line is not power limitedand is considered large enough to be a fire-hazard, the NationalElectrical Code classifies traditional lighting systems as Class 1circuits and thus requires numerous protective measures. For example,traditional lighting systems are required by the National ElectricalCode to have electrical conductors that are installed in the form ofarmored cable or within steel conduits.

FIGS. 1 and 2 depict two traditional lighting systems. FIG. 1 shows atraditional lighting system having six troffers 102 connected inparallel to each other. Each troffer typically includes a ballast (notshown) and is connected to a junction box 104 by a whip

Each junction box 104 is then connected to an ordinary power outlet 108via conduit wire that is housed within a steel conduit 110.

FIG. 2 shows another traditional lighting system having three recessedlight fixtures 202 connected in series. In this traditional lightingsystem, each recessed light fixture 202 includes a junction box 204associated with each fixture and connected to the fixture via a whip206. As in the system of FIG. 1, each junction box is then connected toan ordinary power outlet via conduit wire that is housed within a steelcable.

These and other traditional lighting systems have numerous drawbacks.First, by delivering a line voltage to each fixture, traditionallighting systems provide a shock hazard and thus present a significantdanger during installations. In addition, components such as steelconduit and whips, which are required in Class 1 systems for safetymeasures, are both costly and inflexible. For example, installation ofsteel conduit around obstructions can be time-consuming, and anylast-minute reconfigurations may become very cumbersome.

A solution to many of the problems associated with traditional lightingsystems was introduced by Ole Nilssen in U.S. Pat. No. 4,626,747.Specifically, the Nilssen patent disclosed a lighting system capable ofcomplying with Class 3 power requirements. The Class 3 lighting systemincludes a power supply capable of being connected to an ordinary powerline and converting the non-power limited, low-frequency power linevoltage to a power-limited, high-frequency voltage. The Class 3 lightingsystem also includes a light fixture capable of being connected to thepower supply in a location that may be remote from the power supply.Because of the Class-3 output characteristics of the power supply units,the amount of available power in the Nilssen patent was limited to alevel considered acceptably safe from a fire initiation viewpoint, yetadequate in power to provide ample light from a fluorescent lightingfixture (e.g. 100 Watts).

By using a Class 3 power supply that mounts remotely from the fixture,the lighting system disclosed in the Nilssen patent eliminates the needfor steel conduits, whips and other associated components necessary fortraditional Class 1 lighting systems, reduces material expenses andmanagement/inventory costs, and virtually eliminates trade conflictcallbacks. Due to the high-frequency operation of the Nilssen Class 3system, the lamp transformer within each fixture could be small andlight weight. Combining this miniaturized transformer with the reducedfixture/structural requirements, due to the Class-3 characteristics,permits the lighting fixtures to be particularly compact andlight-of-weight. Furthermore, because of their Class-3 nature, thefixtures in the Nilssen lighting system may also be considered asordinary portable (plug-in) lighting products; which implies that theymay be installed, moved, removed, and/or exchanged by unskilled persons.

However, the Nilssen lighting system did not provide a complete answer.Specifically, the power supply output disclosed in the Nilssen patentwas controlled by providing a constant voltage while limiting the outputcurrent. This approach results in a significant voltage drop alongtransmission cables causing the output of a lamp to vary significantlydepending on its distance from the power supply. In addition, fixturesdesigned to operate with the constant voltage power supply disclosed inthe Nilssen patent require matching tank circuits, which may increaseboth the cost and complexity of the lamp driver circuits.

SUMMARY OF THE INVENTION

The present invention is a flexible cable for a lighting system having apower supply and at least one luminaire. The flexible cable is connectedbetween at least one output of the power supply and the at least oneluminaire, which is coupled to at least one lamp driver. The powersupply includes a power input for receiving a first signal having afirst frequency, and a circuit for converting the first signal to asecond signal.

According to one aspect, the flexible cable comprises an insulatednon-polarized twisted pair of wires for carrying the second signal, andan insulated single wire. A first wire of the twisted non-polarized pairof wires is electrically connected between a loop output of the powersupply and a loop input of the lamp driver, and a second wire of thetwisted pair is electrically is electrically connected between a loopoutput of the lamp driver and a loop return of the power supply. Theuninsulated wire is electrically connected to a ground of the powersupply and a ground of the lamp driver.

The flexible cable is a plenum rated Class 3 cable. The uninsulated wireincludes a 14 AWG ground and the twisted pair of wires includes an 18AWG twisted pair. The insulated and uninsulated wires may be enclosed ina common jacket.

Each flexible cable is also preferably terminated using a self-lockingconnector to allow for easy modular connection between components of thelighting system. This modular connectivity provides for easierinstallation as well as increased flexibility in the reconfiguration andrelocation of lighting fixtures.

According to another aspect, the power supply is designed to physicallymount to a junction box and to convert the ordinary power line signal(typically 60 Hz@120V or 277V) to a high frequency output signal (forexample, 48 kHz). The flexible cable provides the output of the powersupply at a substantially constant current level. In addition, the powersupply also includes circuitry to ensure that the power supply outputsignal is power limited to 100 VA. As the output current is maintainedconstant, the output voltage is then controlled in accordance with theconnected load in order to comply with the power limit requirement.

According to another aspect, the at least one lamp driver is mounted toa fixture and configured to receive the high-frequency output signalfrom the power supply. The lamp driver then uses the power signalprovided via the flexible cable to operate one or more lamps. Each lampdriver may include circuitry configured to operate a specific lamp type.For example, lamp drivers may be configured to operate eitherincandescent, fluorescent, or other type lamps. In addition, each lampdriver may also be connected to the power converter either in parallelor in series.

In comparison to traditional Class 1 lighting systems, the presentinvention results in electrical energy savings, reduced labor, loweredcosts, and additional safety by eliminating the need to run the powerline voltage to each light fixture. In addition, unlike previously knownhigh-frequency Class 3 lighting systems, the constant current powersupply allows for equal light output regardless of cable length andeliminates the need for expensive matching circuitry in the lamp driver.Lastly, the heat dissipation focused at the power supply can be flexiblylocated within a building ceiling spaces away from the fixture to reducethe load demands of the HVAC system.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a prior art lighting system;

FIG. 2 shows another prior art lighting system;

FIG. 3 shows a lighting system according to the present invention;

FIG. 4 shows another lighting system according to the present invention;

FIG. 5 shows a block diagram of one embodiment of a power supply;

FIG. 6 is a circuit diagram of one embodiment of the power supply;

FIG. 7 is a block diagram of one embodiment of a single-lamp driver;

FIG. 8 is a circuit diagram of one embodiment of a single-lamp driver;

FIG. 9 is a block diagram of one embodiment of the lamp driver control;

FIG. 10 is a block diagram of one embodiment of a three-lamp driver; and

FIG. 11 is a circuit diagram of one embodiment of a three-lamp driver.

FIG. 12 is a cross section of one embodiment of a cable.

DETAILED DESCRIPTION

The present invention is a lighting system having a power supply, atleast one luminaire, and a flexible cable for connecting the powersupply to the luminaires. The power supply preferably includes a powersupply input to receive a power line signal, a circuit to convert thepower line signal to a substantially constant-current, high-frequencysignal, and a power supply output to output the substantiallyconstant-current, high-frequency signal. Each luminaire also preferablyincludes a lamp, a housing to hold the lamp, luminaire input to receivethe high-frequency signal from the power supply, and a lamp drivercircuit configured to use the received output signal to operate thelamp.

FIG. 3 shows one exemplary embodiment of the lighting system. In thisembodiment, a junction box 304 is supplied with a power line signal(typically, either a 60 Hz@120V or 277V signal) through a pair of powerline conductors and a safety ground via a steel armored conduit 302. Inthe depicted example, two power supplies 306 are mounted to the junctionbox 304 so that each power supply 306 is operably connected to receivethe power line signal and connected safety ground. It should also beunderstood that instead of physically mounting the power supply to ajunction box, the power supply may instead be configured to receive apower line signal from an ordinary power outlet via a standard malepower plug.

Each power supply 304 includes an output 306 for outputting thesubstantially constant current, high-frequency signal. By using thishigh frequency signal, the power supply can be used to operate aluminaire that is mounted in a remote location from the power supply.For example, the luminaire may be mounted more than 20 feet from thepower supply.

The output from each power supply unit is also power-limited to amaximum of 100 Volt-Ampere in accordance with specifications forClass-3circuits (as defined by the National Electrical Code) and cantherefore be installed without conduit and connected to a luminaire byway of a plug-in light-weight flexible two-wire electric connect cord.Thus, as shown in FIG. 3, each output port is connected via a flexiblecable 308 to a lamp driver (not shown in FIG. 3) located within arespective one of the troffers 310. Although the power supplies areshown with two output ports, the power supply may alternatively includeonly a single output port or more than two output ports.

Each output port in the power supply is also preferably configured tophysically receive and disconnectably connect electrically to a modularconnector at one end of the flexible cable. The other end of the cablealso preferably includes a modular connector configured to be physicallyand electrically received by one of the luminaires. Due to the modularconnection, the power supplies and luminaire may be easily disconnectedand reconnected in order to allow for quicker installation,reconfiguration, and replacement of components.

FIG. 4 shows another exemplary embodiment of the lighting system. Inthis embodiment, a single power supply 404 is similarly connected to ajunction box 402 to receive a power line signal. The power supply 404 isthen connected, via a flexible cable 406, to three recessed lights 408.Each recessed light 408 includes a lamp driver mounted to the fixturehousing. The lamp driver may include as many as two ports, each of whichis capable of disconnectably receiving the flexible cable. Each of theseports can be used either as an input port or an output port.Accordingly, unlike the embodiment shown in FIG. 3 where each of theluminaires is connected to the power supply in parallel (i.e. eachluminaire is connected to a respective output port in the power supply),each of the luminaires shown in FIG. 4 is capable of being connected inseries to one another. Therefore, in this embodiment, it is possible tooperate multiple luminaires from a single output port from the powersupply. The specific number of luminaires that can be connected inseries is based on the wattage of the lamp in each respective luminaireand the power output from the power supply. For example, a 100W powersupply output may be used to power two 42W lamps in series or three 26Wlamps in series.

As noted above, the output from the power supply in the presentinvention is a substantially constant-current output signal.Accordingly, the current of the output signal remains relativelyunchanged throughout a specific load impedance range. For purposes ofthis description, “substantially constant” means the magnitude of therms current varies less than 10% between short circuit and full load. Infact, ideally the only real deviation between short circuit, fullyloaded, and fully loaded with cable included is to the waveshape of thecurrent. The short circuit current waveshape tends to be triangular,reflecting the inductive nature of the driving impedence, while addingload via lamps drivers, cable inductance and capacitance tends to be afiltered sinusoidal current.

The magnitude of the constant-current output from the power supply maybe chosen depending on the specific application and design. Preferably,for a Class 3 system, the current is between approximately 0.67Amps_(rms) and 3.3 Amps_(rms).

In one embodiment, the constant current output is designed to be 1.3Amps_(rms) and the power supply is configured to operate with loadimpedances from 0 to 50 ohms. Under this embodiment, loading the loopwith impedances between 0 and 58 ohms could cause the output voltage tovary from 0V_(rms) to 75V_(rms), and thus vary the output power from 0VA to 100 VA, respectively. Accordingly, the power output of the powersupply would range from an essentially 0 VA short circuit, through the100 VA maximum load for a Class 3 circuit.

Any impedance conditions greater than 58 Ohms, (including open circuit),attempting to push output voltage greater than 75V_(rms), and powergreater than 100VA are then power limited to ensure compliance withClass 3 requirements. This power limitation be accomplished in threedifferent ways. In a first method, the power supply input may be fused.Faults internal to the power supply or externally applied to a portwould then limit the power supply's ability to absorb power from theinput line and deliver it to the output. Various fuse methodologies maybe used. In a second method, an active electronic circuit may beconfigured to monitor the port output and to then trigger a shortcircuit of the output transformer, thus disabling the output providing a“voltage fuse” characteristic.

In a third method, the overall electronic semiconductor and outputtransformer designs may provide an “Inherent Limiting” type protectionas is commonly used in electronic ballast technology. In this approach,the power semiconductor junctions may be selected to begin breakdown at150° C., leading to their failure, which can either disable open a powercircuit or a protective fuse. Alternatively or additionally, thetransformers may be selected and placed in the circuit to inherentlylimit power as the wire becomes substantially more resistive due toheating. Of course, while the power limitation circuitry is preferablylocated in the power supply, it may also be located within other systemcomponents. For example, power limitation methods similar to thosedescribed above may be located in the luminaire instead of the powersupply. A fuse may also be operably located in the flexible cable.

FIG. 5 and 6 show a block diagram and a circuit diagram, respectively,of one exemplary embodiment of a power supply having two output ports.In this embodiment, the power supply includes a first filter 500, arectifier circuit 505, a boost converter 510, a boost converter control515, an inverter 520, an inverter drive oscillator 525, a first LV (“lowvoltage”) power supply 530, a second LV power supply 535, a secondfilter 540, a first port output transformer 545, a first port relay 550,a second port output transformer 555, a second port relay 560, and anoutput relay control 565. For purposes of the block diagram of FIG. 5(as well as those of FIGS. 7 and 10 discussed below), solid linesbetween blocks represent high voltage and power levels, dotted linesrepresent low voltage and signal levels, and dashed lines representisolated class 3 power levels.

The first filter 500 is preferably a 2-Stage EMI filter for minimizingboth common and differential mode interference from being conducted outon the input conductor connections. In one embodiment, the 2-Stage EMIFilter has one power input for receiving the AC power line signal andone power output to the rectifier circuit 505.

As shown in FIG. 6, the input fuse FS101 is the first main component ofthe filter and is in series with the line voltage connection. The fuseFS101 is followed by the first stage of the EMI filter. It consists of asurge arrester VDR101, a Class X capacitor C128, and a bleeder resistorR108 in parallel from fused line to neutral. Both line and neutral arethen series connected through a common-mode choke L101. The common-modechoke L101 is followed by two Class Y capacitors C108 and C129 fromfiltered line and neutral, respectively, through damping resistor R157to the ground. The second stage of the EMI filter begins with a Class Xcapacitor C135 from line to neutral. Class X capacitor C135 is thenfollowed with another common-mode choke L102. The second stage iscompleted with two Class Y filter capacitors C118 and C119 from thefiltered line and neutral to ground.

The rectifier circuit 505 preferably has one main power input forreceiving the signal from the filter 500, one main power output to theboost converter 510. The rectifier circuit 505 also has three lowvoltage resistor feeds to the inverter drive oscillator 525, the boostconverter control 515 and the first LV power supply 530.

As shown in FIG. 6, the rectifier circuit includes a bridge rectifierBR1 to convert sinusoidal voltages on the filtered line and neutral intoa full-wave rectified line of pulsating DC supply. Preferably, thebridge rectifier has a near unity power factor (PF) and a low totalharmonic distortion (THD) of less than 10%. In the preferred embodiment,Sections 505, 510, 515 & 530 are responsible for insuring that the powersupply has a low THD and appears essentially resistive to the powerline. Accordingly, the rectified line voltage appears as a haversinewaveform rectified with respect to circuit ground. The rectifier circuit505 also includes a resistor R106 that functions as the upper end of avoltage divider for sensing the relatively high voltage rectified lineto be fed to the boost converter control 525. Resistors R109 and R110are in series and fed to the first LV power supply 530. Resistors R109and R110 assist the starting of the controller in the boost convertercontrol 525 through the first LV power supply 530. Resistors R146, R147and R148 are the upper-end of a voltage divider for feeding a low-inputvoltage sense signal to the Inverter Drive Oscillator. Filter capacitorC112 mildly filters the higher frequency noise on the pulsating DC.Filter capacitor C112 also acts as a tanking capacitor for the frequencyrange of operation required to perform the power factor correction, yetdoes not appreciably affect the waveform shape of the low frequencyhaversine wave.

The Boost Converter 510 does the initial power processing in the powersupply. The Boost Converter 510 has one main power input for receivingpower from the rectifier circuit 505 and one main power output to theinverter. The Boost Converter 510 also includes one signal input fromthe boost converter control 515, and three signal outputs: the first isLV Power Supply 1 output, the second is the Inverter Drive Oscillatoroutput, and the third is signal output to the boost converter control.The third signal output includes three different sense signals forcontrolling the boost converter, as discussed below.

In the embodiment shown in FIG. 6, the Boost Converter 510 consists offourteen components. Winding L104A of the boost inductor L104 is fedfrom the rectified line to the junction of the Fet transistor TR103drain lead and the rectifier diode D115 anode, which perform the boostfunction by the controlled switching of the boost transistor, thecoincident storing of energy in the boost inductor, and the delivery ofhigher switch frequency pulse voltage than the low frequency rectifiedinput pulse voltage, all via the boost rectifier.

FET transistor switching speed is strictly limited by a snubber networkconsisting of capacitor C137 and resistors R163, R164, R165 and R166.The FET transistor source lead also feeds through a parallel combinationof three resistors R140, R141 and R142, which produce a first sensesignal sent to the Boost Converter Control 515. Another resistor R107 isthe upper end of a voltage divider for sensing the boosted DC outputvoltage for feedback processing by the controller in the Boost ConverterControl, and produces a second sense signals sent to the Boost ConverterControl. Lastly, winding L4B of the boost inductor performs twofunctions. Winding L104B supplies a third sense signal to the controllerof the Boost Converter Control block. Winding L104B also supplies a lowvoltage drive for the first LV Power Supply.

The boost rectifier also feeds an energy storage aluminum electrolyticbulk capacitor C116 to smooth the boosted pulse voltage into a DCvoltage. Resistor R1 assists in starting the half-bridge inverter driveoscillator IC. In addition, the boost inductor is fitted with a thermalfuse. If the inductor exceeds a designated temperature, the thermalfuse—which is preferably wound into the coil of the inductor—will opencircuit the boost inductor. As such, the inductor-fuse combination is anactive limiter of power through the converter.

The first LV power supply 530 and the second LV power supply 535 are lowvoltage power sources for signal circuitry. The main function of thefirst LV power supply 530 is to provide power to the Boost ConverterControl 515, while the main function of the second LV power supply 535is to provide power to the Inverter Drive Oscillator 525 and OutputRelay Control 565.

The first LV power supply 530 includes three inputs. As discussed above,the first LV power supply 530 receives, at the first input, a lowvoltage from the winding L104B of L104 in the Boost Converter. Astart-up current is resistively supplied by the rectifier circuit to thesecond input of the first LV power supply. Auxiliary support current isalso supplied from the second LV Power Supply to the first LV PowerSupply at a third input.

As shown in FIG. 6, the first LV power supply 530 consists of fivecomponents. Capacitor C113, Resistor R112, rectifier diode D111 andZener regulator diode D116 form a standard charge pump circuit. Thisprovides enough energy for the electrolytic storage capacitor C117 tomaintain an appropriate operating low voltage DC for the circuitry ofthe Boost Converter Control.

The second LV power supply 535 comprises six components. The charge pumpsupply is formed by five components: capacitors C103 and C107 rectifierdiode D102, Zener regulator diode D110 and resistor R103. The chargepump requires the high voltage half-bridge to run so that theappropriate voltage can be developed and supplied to the other circuitblocks. The second LV power supply 535 sends power to the LV PowerSupply 1 block via diode D105.

The boost converter control 515 processes the signals sensed from otherblocks in the power supply. The boost converter control includes threeinputs and one output. As shown in FIG. 6, the output of the boostconverter control 535 comes from a L6561 integrated circuit controllerIC1 through a resistor R114 to the gate lead input of the BoostConverter switch Fet transistor. The input from the first LV PowerSupply, discussed above, feeds operating voltage to IC101. The inputfrom the Bridge Rectifier uses resistor R111 as the lower end of thevoltage divider and capacitor C114 as a noise filter. The signalproduced from the sensing of the boost converter input lowers thevoltage level and maintains the low frequency form appropriate forprocessing by the controller. The third input receives the three sensesignals from the boost controller as discussed above. The first is theswitch transistor current sense feedback voltage feeding the currentsense input of IC101. The second uses precision resistors R115 and R139as the lower end of the voltage divider formed in conjunction withpreviously mentioned R107. The signal produced feeds through a parallelcombination of resistor RI51 and signal diode D123 for conditionalfeedback discrimination to the error amplifier within the controller. Italso uses capacitor C136 to pole compensate the frequency response forfeedback control, as well as capacitor C115 in series with resistor R152across C136 to further vary the feedback compensation. Capacitor C139couples feedback to the IC101 multiplier input to minimize the thirdharmonic contribution to THD, (total harmonic distortion). The thirduses resistor R113 to limit the signal sense voltage from the 104B sensewinding. This sense winding provides information to the controller aboutthe state of the L104A winding, the boost inductor itself.

The controller IC101 is a standard Power Factor correction typecontroller for making the supply appear as a resistive load to the line.It also limits the total harmonic distortion of the line current so asto not strain the line system with noise and other obnoxious currentwaveforms. The IC101 pumps the appropriately timed switch signals tooperate in the boost converter in critical conduction mode and achievethe benefits previously mentioned.

The inverter 520 is preferably a half bridge-inverter. The inverter hasone main power input which is the boosted DC voltage output of the BoostConverter block and one main power output that drives the second filter540. The half-bridge inverter also includes three output feeds thattransmit three high voltage signals to other blocks. Two of thesesignals are used to drive charge pump circuits in the second LV PowerSupply and the Output Relay Control. The third feeds the Half-BridgeInverter Drive Oscillator. The inverter 520 also receives two inputsfrom the Inverter Drive Oscillator 525. These are signals for operatingthe half-bridge switch transistors. One has to be high voltage levelshifted to drive the upper switch in the half-bridge. The other is lowvoltage and drives the lower ground referenced switch in thehalf-bridge.

As shown in FIG. 6, the inverter consists of five components. Two switchFET transistors TR101 and TR102 are configured in a typical half-bridgeconnection. DC blocking capacitors C105 and C106 are configured toprovide a half-boost voltage center-tap reference for the half-bridgeload. In addition, capacitor C120 is a Class Y safety noise bypassbetween chassis ground and the effective AC grounded center-tap of C105and C106.

The inverter drive oscillator 525 includes a IR2153 high voltageintegrated circuit IC102, which is basically a combination of anoscillator and a half-bridge driver. The high voltage integrated circuitIC102 feeds gate signals to the half-bridge FET transistors viaresistors R104 and R105. The frequency of the half-bridge is set atIC102 via capacitor C101, resistor R102, and variable resistor R117.Adjustments of R117 also sets the value of constant output current, aswell as tunes the open circuit output transient turn-on response.Blocking diode D112 and storage capacitor C109 isolate and filter thesecond LV Power Supply signal providing IC operating voltage. Thisvoltage is Zener regulator diode D108 clamped and capacitor C138 highfrequency bypassed. The level-shift capacitor C102 charges through diodeD101 from the IC supply voltage during lower half of a switching cycle.The other components in the inverter drive oscillator include fourresistors R124, R125, R136 and R145, Zener clamp diode D109, storagecapacitor C111 and logic switch transistors TR106 and TR107 configuredfor low VAC input detection and IC102 shutdown.

The resonant filter 540 has one main power input from the Inverter 520,which is the half-bridge output voltage. The resonant filter 540 alsohas one main output to the first port output transformer across theresonant capacitance. The resonant filter 540, when adjusted to theoptimal frequency, provides power to the first and second port outputtransformers. In addition, in the normal load range, the resonant filterremoves the high frequency harmonics of the square wave generated by thehalf-bridge to the fundamental frequency sine wave component. Theresonant filter 540 includes a resonant inductor L105 in series with aresonant capacitor C130. However, if the power supply is configured tobe used with 120V input rather than a 277V input, the filter mayalternatively be comprised of a resonant inductor L105 in series withfour parallel-connected resonant capacitors C124, C125, C126, and C127,as shown in FIG. 6. The series resonant, parallel loaded connectedfilter AC grounds at the center-tap point of C105 and C106.

The first port output transformer 545 is comprised of a transformerTFR101. The transformer TFR101 has three windings. The filter outputruns through the series connected primaries of the first and second portoutput transformers, thus feeding the second port output transformer.Primary transformer shutdown control is achieved by the input from thefirst port relay. Each port output transformer has two secondarywindings. The first is a TFR101B sense winding for feeding a signal tothe output relay control. The TFR101D second winding is thecenter-tapped port output. Since the output port winding iscenter-tapped and the center-tap is connected to chassis ground, eitherend of the winding produces a Bi-phase or balanced voltage.

The first port relay 550 includes a relay part RL101 across the TFR101Aprimary of TFR101 and coupled to the second port relay across theTRF102A primary of TRF102. It is activated via the output relay control.It also receives a signal from the output relay control 565 to short theprimary of TFR101 that disables the first output port. This occurs onlyif conditions measured within the Output Relay Control block warrantport shutdown.

The second port output transformer reference is TFR102. Since it has aprimary TFR102A in series with the TFR101 it shows a power input fromthe first port output transformer block. The two series connectedprimaries terminate at the same center-tap of C105 and C106 because theconnection is in parallel with the resonant capacitance in the resonantfilter block. The second port output secondary is TFR102D while thesense secondary is TFR102B. Although the second port output transformerand the first port output transformer are illustrated in FIG. 6 as beingin series, the second output transformer may also be designed to be thesame as the first port output transformer.

The second port relay 560 performs in a similar manner as the first portrelay. The second port relay includes a relay part RL102 across theTFR102A primary of TFR102 and coupled to the first port relay across theTRF101A primary of TRF101. It is activated via the output relay controlblock. It also receives a signal to short the primary TFR102A of TFR102that disables second output port, which occurs only if conditionsmeasured within the output relay control block warrant port shutdown.

The output relay control 565 is responsible for monitoring the operationof the first and second ports. Both the first and second porttransformer blocks 545 and 555 provide signals to the output relaycontrol from sense windings that monitor output port voltage andtherefore load conditions. The second LV power supply 535 provides lowvoltage power to the output relay control. The inverter 520 provideshalf-bridge output to a local charge pump, and a supply voltagereference to drive the relay control transistors and relay controlwindings. Both the first and second port relays 550 and 560 are thenprovided control signals from the output relay control block.

In one embodiment, the output relay control includes fifty-twocomponents. A high frequency bypass capacitor C104 is provided on thesecond LV power supply rail, local to the relay control circuitry. Thehalf-bridge output driven charge pump consists of capacitors C131, C132,C110 and rectifier diodes D104 and D110. This provides an appropriatevoltage to run the two common-collector relay switch transistors, TR104and TR105 and/or the relay control windings, with a provisional Zenerdiode D118 clamp in series with the upper control RL101A winding ofrelay RL101. Resistor R122 is a biasing resistor for TR104 and TR105.The output transformer sense windings TRF101B and TRF102B are diode D106and D107 rectified and the signals are divided down with resistors R118,R119, R120, R121, R133 and R134 and clamped with Zener diodes D119 andD120. A small delay is then inserted consisting of resistors R137 andR138 and capacitors C133 and C134. These signals provide DC referencevoltages representative of the load state of the output ports. ResistorR135, Zener regulator diode, D117 and high frequency bypass capacitorC123 are configured to create a simple reference voltage fed viaresistors R143 and R144 for use in comparison with the port state DCreference voltages. A dual IC operational amplifier IC103 is used toprocess the comparison via either IC103A or IC103B, depending on theport. The differential amplifiers are control loop compensated withcapacitors, C121 and C122. Diodes D113 and D114 are configured to latchthe amplifier outputs high if the signal level goes high. Port DCreferences are fed to appropriate amplifiers via resistors R149 andR150. Two networks consisting of resistors R158 and R159 and diodes D121and D122 couple the port DC reference voltages to the main reference.This allows transient clamping of the port DC reference voltages withrespect to the common reference. The outputs of both amplifiers feedindividual resistor dividers consisting of resistors R129, R130, R131and R132 for scaling to buffer transistors TR109 and TR1010. TransistorsTR109 and TR1010 are also biased with resistors R126, R127 and R123,R128, respectively. Transistor TR109 drives transistor, TR108 whichcontrols the upper TR104 relay switch transistor state. It is alsocoupled through resistor R116. Transistor TR110 directly controls thelower TRI05 relay switch transistor state. When in proper load range,the relays are signaled to remain open. When out of load range, signalsto the relays short the appropriate primary or primaries to extinguishone or both port outputs. This way a port can run normally even if theother is faulted. Strategic time constants implemented at eachdifferential amplifier enable a response time, tuned for limiting portoutput in the required voltage and power ranges. It also limits theoutput transient response at power converter turn-on. A triggeredshutdown state is latched till a cycle of input to the power supply canbe performed.

In one embodiment, the component values used in the power supply in FIG.6 are as detailed in Appendix A.

FIGS. 7 and 8 illustrate a block diagram and a circuit diagram,respectively, for one exemplary embodiment of a single-lamp driver. Asshown in FIG. 7, the single-lamp driver 600 includes a lamp drivertransformer 605, a lamp current sense transformer 610, and LV powersupply transformer 615, an LV power supply 620, a filament transformerrelay 625, a filament driver transformer 630, and a lamp driver control635.

As shown in FIGS. 7 and 8, the loop current generally drives a pair ofbalanced primaries on the Lamp Driver Transformer 605 (TX201 in FIG. 8)in series with the primary of the LV Power Supply Transformer 615 (TX204in FIG. 8). In parallel with the balanced primary windings of the LampDriver Transformer is the series connection of the primary of theFilament Driver Transformer 630 (TX202 in FIG. 8) and the switch of theFilament Transformer Relay 625 (RLY201 in FIG. 8). A return for the portloop current is provided since these designs offer a daisy chainconnection option to another similar driver, or must be short circuitterminated.

As shown in FIG. 4, the short circuit termination may be accomplishedvia a terminator cap attached to the output port of the lamp driver whenthe lamp driver is not connected to any subsequent luminaires.Alternatively, each lamp driver may be capable of performing automaticshort circuiting. For example, a port may remain short-circuited untilthe presence of a connected cable is detected. Such functionality may beperformed either mechanically or electrically and eliminates the needfor a separate terminator cap. In addition, an automatic shortcircuiting circuit may also be configured to allow a user to initiate ashort circuit at a port even if that port is connected to another lampin the series. As a result, any lamps downstream of the short-circuitedport can be turned off without affecting the power delivered to lampsupstream of the short circuit.

The secondary of the lamp driver transformer TX201 is situated acrossthe series connection of the Lamp Current Sense Transformer TX203 andthe across lamp output. In this way switching of the relay to an openstate at lamp ignition disables the filament drive and resets the lampoutput for the proper voltage and current operation.

The lamp current sense transformer 610 enables establishment anddetection of proper lamp functioning. As previously mentioned, the lampoutput is series connected through the Lamp Current Sense TransformerTX203. The secondary of the current sense transformer signals the LampDriver Control 635.

The LV power supply transformer TX4 steps loop current to an appropriatevalue to operate the LV Power Supply and subsequent loads. Since itsprimary is in series with the loop current, it can be scaled to provideappropriate low voltage power to run the control circuitry. In oneembodiment, the ratio of the primary to secondary turns are 8:88 forTX201, 1:3 for TX202, 6:1 for TX203 and 1:20 for TX204.

The LV power supply 620 consists of four components configured forcharge pumping and energy storage. Capacitor C204, Zener diode, ZD201and rectifier diode D205 connect to form the charge pump portion of thesupply. Capacitor C203 stores energy and averages the rectified outputof the charge pump. Capacitor C203 also provides voltages to operate thecircuitry of the Lamp Driver Control block.

The input of the filament transformer relay RLY201 switches power fromthe loop current to the Filament Drive Transformer. The filamenttransformer relay RLY201 has one signal level input from the Lamp DriverControl and is set-up in the normally closed mode. When activated, itopens the filament transformer primary, eliminating the filament powerdelivery, as well as releasing its shorting of the balanced primary ofthe Lamp Driver Transformer.

The filament driver transformer 630 consists of three secondarywindings. The primary winding connection was previously discussed. Twosecondary windings provide filament heating current. This occurs onlywhen the RLY201 relay is closed. The third winding provides feedback tothe Lamp driver Control block.

The Lamp Driver Control 635 makes the interpretations about what stateto assume based on lamp load, daisy chain, and any other designconsiderations. FIG. 9 illustrates a block diagram of one embodiment ofthe lamp driver control block. One component of the Lamp driver controlis an integrated circuit U201 (shown in FIG. 8) which consists of fourdiscrete comparator sections. The other components form a lamp currentdetection and processing circuit 905, a filament drive transformerdetection and processing circuit 910, relay control winding drive outputprocessing circuit 915, and over-temperature shutdown circuit 920.

The over-temperature shutdown circuit 920 controls the shutdown of theLV power supply 620 and consists of a positive temperature coefficientresistor PTC201, bias resistors R229 and R230, switch transistor pairQ204/205, and bypass capacitor C217. Simply, PTC201 monitors the ambienttemperature within the driver. R229 and PTC201 form a voltage dividerwith respect to the LV Power Supply rail. It feeds the transistors ofthe Q204/205 pair, shorting the output of the LV Power Supply. Without asource of power the filament relay closes, disabling the lamp output.

The relay control winding drive output processing circuit 915 includes12 components. The PNP transistor Q202 is responsible for directlysourcing holding current to the relay control winding. Capacitor C216noise filters the relay control winding, along with half of the dualdiode D206/207. Q202 is controlled by NPN transistor Q201. Thesetransistors are both biased through resistor R208. Signaling to the baseof Q201 is coupled through resistor R225. This resistor also feedsthrough a parallel combination of bias resistor R223 and speed-upcapacitor C215 to stabilize the collector of Q202 and provide additionaldrive to open the relay. The time constant of resistor R201 andcapacitor C201 determine the program starting time for filament heating.They also couple in at R225 and the output of the current sense detectsection. The emitter of Q201 is level set via resistor R6 and Zenerdiode ZD203. Overall, the purpose of the relay control winding drive 915is to provide current to activate the normally closed filamenttransformer relay. The current sense detection circuit directly controlsthat drive, while the filament detection resets a latch within thecurrent detection to allow restarting of the control winding drive.

The filament drive transformer detection and processing circuit 910 iscomprised of twenty four components. Load capacitor C212 is in parallelwith the filament transformer detection secondary. A charge pumpconverter consisting of capacitor C211 and dual diode D212/213. Filtercapacitor C210 and preload resistor R222 complete the formation of thelamp detection signal. The signal is then fed through resistor R226 tothe non-inverting terminal of a single comparator section. Thisnon-inverting input is clamped via Zener diode, ZD202. A voltage dividerconsisting of resistors R220 and R221 reference sets the associatedinverting terminal of the same comparator section. The comparator outputdrives PNP transistor Q203 coupled through resistor R219. Timingcapacitor C209 is across the emitter and collector terminals of Q203.Resistor R211 determines the rate at which C209 charges or dischargesonce Q203 is signaled to turn off or turn on, respectively. Dual diodesD208/209 are configured to prevent the voltage across R211 from extremenegative voltage excursions and allow a low signal at the collector ofQ203 to control the next coupled comparator section. Resistors R212 andR213 are responsible for set-up of the reference voltage on thenon-inverting pin of the pulse generator configuration of the secondcomparator section. This generator can signal the current sensedetection and processing circuit latch through diode D214. ResistorsR217 and R218, each in series with respective diodes of dual diodeD210/211, act as bias sources for the comparator output. Feed forwardthrough resistor, R216 from the non-inverting terminal to the junctionof one bias network enables a two level variable reference point forhysteresis. This enables the other output bias network to charge througha time constant associated with resistor R215 and capacitor C208. TheR215 and C208 network couples into the inverting pin of the comparatorthrough resistor R214 enabling a low pulse on the generator output. Thiscycle repeats until Q203 is turned off long enough to charge C209,pulling the inverting input to a low state and preventing C208 fromrecharging. The overall function of this circuit is to reset a latch inthe current detector section with a low pulse from the filament detectsection. This occurs because C208 charges through R215 once the controlwinding drive turns on and opens the relay. After C208 charges, ittriggers a pulse, restarting a turn on cycle in the relay controlwinding drive output. This will happen for a number of cycles allowed bythe R211 and C209 time constant.

The current detection and processing 905 consists of eighteen parts. Thefunctioning of capacitors C213, C207 and C205, dual diode D203/204, andresistor R210 is exactly the same as their counterparts described in theprevious section. They create a signal representation of the lampoperating current. In a first comparator section, the non-inverting pinreference is set up via resistors R203 and R228 and filter capacitorC214. A second comparator section is a resettable latch. The output iscoupled through one diode of the dual diode D201/202 to the R225 of therelay control driver. A resistor divider, resistors R202, R204 and R205,is used to couple through two signals to both the inverting andnon-inverting terminals of the latch via resistors R207 and R224. Thiscreates a window for the normal range of lamp current operation.Shutdown for the lamp end-of-life rectification mode is enabled byforcing the latch to set via the current transformer feedback windingand signal processing. Resistor R227 in series with the other diode ofD201/202 feed the non-inverting signal to the output to insure latchingof the output once it has gone low. Capacitors C206 and C202 are fornoise filtering. Resistor R209 and the other diode of dual diodeD206/207 are in series and can sense drive for the relay controlwinding, so that the relay can set the latch if the current in the lampis not detected and the relay is open. As previously mentioned, thissection directly controls the relay control winding drive output. Themain latch has the power to signal close the relay if a lamp is removedduring operation, a lamp fails for end-of-life rectification, a lamp wasnever present, or lastly, a lamp was present but does not start. It isonly when the lamp is present, it starts, and it runs that the latchdoes not trigger.

In one embodiment, the component values used in the lamp driver in FIG.8 are as detailed in Appendix B.

FIGS. 10 and 11 illustrate a block diagram and a circuit diagram,respectively, of one embodiment of a three-lamp driver 1000. Thethree-lamp driver includes a LV power supply transformer 1005, an LVpower supply 1010, a first lamp driver transformer 1015, a first drivertransformer relay 1020, a first driver relay control 1025, a second lampdriver transformer 1030, a second driver transformer relay 1035, asecond driver relay control 1040, a third lamp driver transformer 1045,a third driver transformer relay 1050, and a third driver relay control1055.

The LV Power Supply Transformer 1005 (TX302 in FIG. 11) has its primaryin series with the primaries of the first lamp driver, the second lampdriver, and the third lamp driver transformers. Loop current runsthrough these primaries. The LV Power Supply transformer TX302 sends lowvoltage power to run the circuitry of the three Lamp Driver RelayControl blocks. In one embodiment, the primary to secondary turn ratiois 2:28.

The LV Power Supply 1010 receives input from the LV Power SupplyTransformer 1005, the first lamp driver transformer 1015, the secondlamp driver transformer 1030, and the third lamp driver transformer1045. The LV Power Supply has three main outputs. Each output consistsof two different voltage signals sent to each of the three sequentialrelay control blocks.

The LV Power Supply 1010 consists of eleven components. The first threeare capacitor C303 , half of a dual rectifier diode D303/304, and Zenerdiode ZD301 configured in a charge pump configuration. This feeds asmall energy storage capacitor C304 setting up a low voltage powersource to run the control circuitry of the relay control block. ResistorR310 is in series with the other half of the dual diode D303/304,feeding the LV Power Supply rail from the first lamp driver transformersense winding. Resistors R311 and R312 are in series with each end ofanother dual rectifier diode D305/306. This network similarly feeds theLV Power Supply rail from the second lamp and the third lamp drivertransformers, respectively. The last two components are resistors R301and R302 which form a voltage divider to create a comparator referencesignal for the first, second, and third lamp driver relay controls.

The first lamp driver transformer 1015 (TX301A in FIG. 11) has itsprimary in series with the primaries of the second lamp drivertransformer 1030, the third lamp driver transformer 1045, and the LVpower supply transformer. Loop current runs through these primaries. Thefirst lamp driver transformer TX301A sends output to a first lamp viaits main secondary winding. It also sends signals to the first lampdriver relay control 1025 and the LV power supply 1010 via an additionalsecondary winding. It receives a shutdown from the first lamp drivertransformer relay 1020 in the form of a short-circuiting of thetransformer primary winding. In one embodiment, the primary to secondaryturn ratio of TX301A is 25:188.

The first lamp driver transformer relay 1020 has one signal input andone output. The input is a signal that allows the relay to remain open,or if necessary, closed. The output uses the relay switch to short thedriver transformer primary, terminating the main secondary windingoutput to its associated lamp. This eliminates voltage availability atthe lamp sockets, for safety during lamp-out and re-lamping situations.

The first lamp relay control 1025 has one main input and one mainoutput. The input really consists of two signal inputs from the LV PowerSupply block, as discussed above. The output feeds voltage to signal thecontrol winding of the first lamp driver transformer relay. The outputsignals the relay to close if the lamp fails to ignite or if a lamp isremoved during operation.

The first lamp relay control 1025 contains thirteen components, alongwith a comparator section that is part of integrated circuit U301. TheU301 IC shares comparator sections with the second and third lamp driverrelay controls, operating in each section in a hysteretic invertingmode. Resistors R308A and R309A divide down the sense signal from thedriver transformer. It is followed by capacitor C301A and dual rectifierdiode D301/302A configured as a charge pump to create a DC signal todetect lamp operation and/or lack thereof. The charge pump feedsresistors R306A and R307A in series, with a Zener diode clamp ZD302Aacross R306A, to the inverting comparator input. The signal there isnoise filtered to ground, as well time constant set-up, by capacitorC302A. Differential mode noise is bypassed across the inverting andnon-inverting comparator inputs by capacitor C306A. In addition,resistor R304A couples in the divided LV Power Supply reference signalfrom the LV Power Supply. The same divided reference signal is coupledto the non-inverting comparator input through resistor R305A along withhysteretic feedback resistor R303A. This comparator section controls thebase of the PNP relay control winding drive transistor Q301A. The Q301Atransistor is turned on when the comparator sinks current, enabling therelay control winding to signal a relay closure. Q301A also latches thecomparator into the low state for the duration of driver operation.Cycling of the input loop current to the driver resets the comparator.

The second and third lamp driver transformers, transformer relays andrelay controls function in a similar manner to those of the first lampdiscussed above and serve to operate a second and third lamp,respectively. In FIG. 11, components that function similar to thosediscussed above for the first lamp are designated with the letter “B”for the second lamp, and “C” for the third lamp. For example, componentsQ301A, Q301B, and Q301C in FIG. 11 are part of the first lamp relaycontrol, the second lamp relay control, and the third lamp relaycontrol, respectively.

In one embodiment, the component values used in the lamp driver in FIG.11 are as detailed in Appendix C.

FIG. 12 illustrates one embodiment of a flexible cable 1200 that may beused to connect components of the present system. The flexible cable1200 is preferably a plenum rated Class 3 cable. According to one aspectof the invention, the cable includes a first leg 1202 having aninsulated non-polarized twisted pair of wires and a second leg having anuninsulated single wire 1204. In one embodiment, the twisted pair is 18AWG bare copper wire and the uninsulated single wire is preferably 14AWG bare copper wire. The twisted pair is also preferably constructed tohave a minimum of 1.27 twists/inch and a capacitance of 19+/−3picofarads per foot.

In one embodiment, the insulation 1206 surrounding each pair of thetwisted pair is comprised of Halar and has a thickness of 0.01 inchesNom. The first and second legs are also preferably provided with acommon jacket 1208 having a narrow web 1210 between the first and secondlegs. In one embodiment, the common jacket has a thickness of 0.018inches Nom.

While various embodiments of the application have been described, itwill be apparent to those of ordinary skill in the art that many moreembodiments and implementations are possible that are within the scopeof this invention. For example, while the system described above isgenerally used with a constant current signal at a relatively constantfrequency, it is noted that the frequency of the constant current signalneed not be fixed. For example, the frequency may be changed duringoperation to provide dimming functionality. If the lamp driver includesa ballasting circuit, the frequency of the constant current signal mayalso be fluctuated to provide lamp ignition. Accordingly, the inventionis not to be restricted except in light of the attached claims and theirequivalent. APPENDIX A R101 180 kΩ R102 13 kΩ R103 100 Ω R104 10 Ω R10510 Ω R106 1.2 MΩ R107 1.2 MΩ R108 1.2 MΩ R109 68 kΩ R110 68 kΩ R111 12kΩ R112 47 Ω R113 68 kΩ R114 22 Ω R115 7.51 kΩ R116 7 kΩ R117 4.7 kΩR118 150 kΩ R119 150 kΩ R120 43 kΩ R121 43 kΩ R122 10 kΩ R123 10 kΩ R12410 kΩ R125 10 kΩ R126 10 kΩ R127 10 kΩ R128 10 kΩ R129 1 kΩ R130 1 kΩR131 9.1 kΩ R132 9.1 kΩ R133 1.8 kΩ R134 1.8 kΩ R135 1 kΩ R136 1 kΩ R13722 kΩ R138 22 kΩ R139 51.1 Ω R140 33 Ω R141 33 Ω R142 33 Ω R143 38 kΩR144 68 kΩ R145 8.2 kΩ R146 8 kΩ R147 8 kΩ R148 8 kΩ R149 10 kΩ R150 10kΩ R151 75 kΩ R152 120 kΩ R153 27 Ω R154 27 Ω R155 27 Ω R156 27 Ω R1574.7 Ω R158 1 kΩ R159 1 kΩ C101 1 nF C102 100 nF C103 100 nF C104 100 nFC105 470 nF C106 470 nF C107 1.5 nF C108 2.2 nF C109 22 uF C110 47 uFC111 47 uF C112 1 uF C113 1.5 nF C114 10 nF C115 220 nF C116 47 uF C11722 uF C118 2.2 nF C119 2.2 nF C120 2.2 nF C121 100 nF C122 100 nF C12310 nF C124 4.7 nF C125 4.7 nF C126 4.7 nF C127 4.7 nF C128 470 nF C1292.2 nF C130 15 nF C131 1 nF C132 1 nF C133 1 uF C134 1 uF C135 1 uF C1361 nF C137 220 pF C138 100 nF C139 100 nF

APPENDIX B R201 3.3 MΩ R202 33 kΩ R203 2.2 MΩ R204 22 kΩ R205 22 kΩ R20633 kΩ R207 1 MΩ R208 22 kΩ R209 100 kΩ R210 100 kΩ R211 1 MΩ R212 2.2 MΩR213 2.2 MΩ R214 2.2 MΩ R215 10 kΩ R216 1 MΩ R217 100 kΩ R218 1 MΩ R21947 kΩ R220 100 kΩ R221 39 kΩ R222 1 MΩ R223 10 MΩ R224 1 MΩ R225 2.2 MΩR226 15 kΩ R227 220 kΩ R228 1.5 MΩ R229 100 kΩ R230 5.1 kΩ C201 1 uFC202 330 nF C203 10 uF C204 33 nF C205 100 nF C206 1 nF C207 33 nF C2081 uF C209 10 uF C210 470 nF C211 3.3 nF C212 0.47 uF C213 0.1 uF C214470 nF C215 470 pF C216 10 nF C217 10 nF

APPENDIX C R301 10 kΩ R302 8.2 kΩ R303A 1 MΩ R303B 1 MΩ R303C 1 MΩ R304A100 kΩ R304B 100 kΩ R304B 100 kΩ R305A 220 kΩ R305B 220 kΩ R305C 220 kΩR306A 150 kΩ R306B 150 kΩ R306C 150 kΩ R307A 100 kΩ R307B 100 kΩ R307B100 kΩ R308A 10 kΩ R308B 10 kΩ R308C 10 kΩ R309A 3.3 kΩ R309B 3.3 kΩR309C 3.3 kΩ R310 220 kΩ R311 220 kΩ R312 220 kΩ C301A 10 nF C301B 10 nFC301C 10 nF C302A 220 nF C302B 220 nF C302C 220 nF C303 100 nF C304 100uF C306A 1 nF C306B 1 nF C306C 1 nF

1. A flexible cable for a lighting system having a power supply and atleast one luminaire, the power supply including a power supply input toreceive a first signal having a first frequency and a circuit forconverting the first signal to a second signal, and the at least oneluminaire coupled to a lamp driver, the cable comprising: a first leg ofwires for carrying the second signal having a first wire electricallyconnecting a loop output of the power supply to a loop input of the lampdriver and a second wire electrically connecting a loop output of thelamp driver to a loop return of the power supply; and a second leg ofwires electrically connected to a ground of the power supply and aground of the lamp driver.
 2. The flexible cable of claim 1, wherein thefirst leg of wires comprise an insulated non-polarized twisted pair ofwires, and the second leg of wires comprises an uninsulated wire.
 3. Theflexible cable of claim 2, wherein the insulated non-polarized twistedpair of wires and the uninsulated wire are housed only in a flexiblejacket between the power supply and the lamp driver.
 4. The flexiblecable of claim 3, wherein the flexible jacket includes a narrow webportion to separate the insulated non-polarized twisted pair of wiresfrom the uninsulated wire.
 5. The flexible cable of claim 4, wherein theinsulation surrounding the non-polarized twisted pair of wires iscomprised of Halar.
 6. The flexible cable of claim 5, wherein thetwisted pair has about 1.27 twists per inch or greater.
 7. The flexiblecable of claim 6, wherein the twisted pair of wires is 18 AWG barecopper wire.
 8. The flexible cable of claim 7, wherein the uninsulatedwire is 14 AWG bare copper wire.
 9. The flexible cable of claim 1,wherein the flexible cable further comprises modular connector.
 10. Theflexible cable of claim 2, wherein the insulation surrounding thenon-polarized twisted pair of wires is comprised of Halar.
 11. Theflexible cable of claim 2, wherein the twisted pair has about 1.27twists per inch or greater.
 12. The flexible cable of claim 2, whereinthe twisted pair of wires is 18 AWG bare copper wire.
 13. The flexiblecable of claim 2, wherein the uninsulated wire is 14 AWG bare copperwire.
 14. The flexible cable of claim 1, wherein the second frequency isapproximately 48 kHz.
 15. The flexible cable of claim 1, wherein thesecond signal has a substantialy constant current and a second frequencydistinctly higher than the first frequency.
 16. The flexible cable ofclaim 15, wherein the substantially constant current is between about0.67 A rms and about 3.3 A rms.
 17. The flexible cable of claim 15,wherein the substantially constant current is approximately 1.3A rms.18. The flexible cable of claim 1, wherein the second signal has a powerfactor greater than 0.98.
 19. The flexible cable of claim 1, wherein thesecond signal has a bi-phase voltage.
 20. The flexible cable of claim 4,wherein the narrow web portion has a thickness of approximately 0.018inches nominal.
 21. The flexible cable of claim 5, wherein theinsulation has a thickness of 0.01 inches nominal.
 22. The flexiblecable of claim 2, wherein the twisted pair of wires has a capacitance ofapproximately 19 picofarads per foot.
 23. A flexible cable forconnecting a constant current power supply to a lamp driver, the cablecomprising: an insulated non-polarized twisted pair of wires, a firstwire of the twisted pair electrically connected to a constant currentloop output of the power supply and a second wire of the twisted pairelectrically connected to the constant current loop return of the powersupply; and an uninsulated wire electrically connected to a ground ofthe power supply and a ground of the lamp driver.
 24. The flexible cableof claim 23, wherein the insulated non-polarized twisted pair of wiresand the uninsulated wire are housed only in a flexible jacket betweenthe power supply and the lamp driver.
 25. The flexible cable of claim24, wherein the flexible jacket includes a narrow web portion toseparate the insulated non-polarized twisted pair of wires from theuninsulated wire.
 26. The flexible cable of claim 25, wherein theinsulation surrounding the non-polarized twisted pair of wires iscomprised of Halar.
 27. The flexible cable of claim 26, wherein thenon-polarized twisted pair has about 1.27 twists per inch or greater.28. The flexible cable of claim 27, wherein the twisted pair of wires is18 AWG bare copper wire.
 29. The flexible cable of claim 28, wherein theuninsulated wire is 14 AWG bare copper wire.
 30. The flexible cable ofclaim 23, wherein the flexible cable further comprises modularconnector.